At room temperature (25°C), the Diels-Alder cycloaddition between cyclopenta-1,3-diene and 1H-pyrrole-2,5-dione predominantly yields the endo-adduct product. However, when the reaction is carried out at an elevated temperature of 90°C, the major product obtained is the exo isomer instead. Further investigations revealed that the initially formed endo isomer undergoes isomerization to the more stable exo isomer at 90°C.
Illustrate and label the structures of both the endo and exo stereoisomers resulting from the Diels-Alder reaction between cyclopenta-1,3-diene and 1H-pyrrole-2,5-dione.